Field of the Invention
The present invention relates to new and improved processes for the preparation of alkyl or aryl phosphonothioic dihalides, and phosphinothioic monohalides.
The Prior Art
Alkyl phosphonothioic dihalides have been prepared in the prior art by reacting alkyl halides with phosphorous trihalides in the presence of aluminum chloride, followed by sulfurization of the reaction product. The alkyl halide/phosphorus trihalide reaction proceeds at room temperature according to the formula set forth in Heuben-Weyl, Methoden der Organis Chenchemie at Volume 12, Part 1, (1956) at page 396: EQU XR--Cl + PCl.sub.3 + AlCl.sub.3 .fwdarw. XR - PCl.sub.4.AlCl.sub.3 I.
the Heuben-Weyl reference also notes that the reaction has been attempted in the absence of the aluminum chloride catalyst with little success. The reaction has the disadvantage that one mole of aluminum chloride is lost for each mole of product prepared.
More recently, the prior art has taught that alkyl or aryl thiophosphorus halides can be prepared by an autoclave process at 200.degree. C. to 450.degree. C. under at least autogenous pressure. Various reactants can be used as outlined in the following reaction sequences:
__________________________________________________________________________ RH + P (S) X.sub.3 .fwdarw.RP (S) X.sub.2 + HCl (U.S. Pat. 3,790,629) 3RX + 3ZP (S) X.sub.2 + 2P.fwdarw.3RP (S) XZ + 2PX.sub.3 (U.S. Pat. 3,726,918) RSaR + PX.sub.3 + (Sulfur Source).sub.2-a + P.fwdarw.RP (S) X.sub.2 a = 1, U.S. Ser. No. 551,805 a = 2, U.S. Ser. No. 548,650 Filed: 2/20/75, Toy and Uhing Filed: 2/10/75, Toy and Uhing RX + P (S) X.sub.3 + S.fwdarw.RP (S) X.sub.2 + SX.sub.2 (U.S. Pat. 3,726,918) __________________________________________________________________________
The thiophosphoryl halide used in these reactions can be prepared in situ by the reaction of phosphorus trichloride and sulfur from a source of available sulfur. The disclosures of the above noted patents and applications are incorporated herewith by reference.
Each of these reactions is plagued by low yields, and by-product formation. For instance, the RH/P(S)X.sub.3 reaction disclosed in U.S. Pat. No. 3,790,629 can be operated successfully on a laboratory scale but the laboratory process cannot be economically scaled up to plant scale. In the laboratory, the reaction was conducted with large excesses (150%) of hydrocarbon (See Example 1 of U.S. Pat. No. 3,790,629). A yield of RP(S)X.sub.2 of 70% was obtained. It is indicated that further increases could be obtained by recycling by-product R.sub.2 P(S)X. Since the price of the hydrocarbon has risen significantly and since government regulations may not allow venting the excess hydrocarbon into the air, any manufacturing operation must include a reclaimation or disposal stage for the hydrocarbon. Reclaimation of the hydrocarbon would require the removal of entrained HX by-product from the hydrocarbon waste stream. Disposal would involve burning a reactant whose price is significant to the economic viability of the process.
An attempt to reduce the quantity of hydrocarbon used in the reaction was unsuccessful. Yields were lowered substantially and a large quantity of by-product residue including solid residues was obtained.
A portion of the problem can be overcome by recycling the by-product R.sub.2 P(S)X as taught in U.S. Pat. No. 3,790,629. However, this requires a further distillation step beyond product separation. The problem of solid and liquid residues as well as low yields would not be overcome.
Similarly, in the other named reactions, yields as well as by-products accumulation can be a problem.
It has now been found that yields in these reactions can be easily increased without extensive processing changes. In most instances, by-product accumulation is reduced or in some cases essentially ceases.